Polystyrene color stabilized with trialkyl phenol and a triazine



United States Patent 3,134,749 POLYSTYRENE COLOR STABILEZEE) WITH TRI-ALKYL PHENOL AND A TRIAZINE Leo Costello, South Bound Brook, and JeromeL. Dunn, Somerviile, N.J., assignors to American Cyanamid Company, NewYork, N.Y., a corporation of Maine No Drawing. Filed Jan. 30, 1%2, Ser.No. 169,954 6 Claims. 81. 26045.8)

This invention relates to protecting polymeric styrene compositionsagainst development on aging of excess coloration, particularly thatproduced by exposure to incident ultraviolet light. More particularly,it is concerned with a unique protective method for such compositionswhich method consists in disseminating therethrough a small amount of aprotective composition consisting essentially of a selected minor amountof a suitable tri-alkyl phenol and a major amount of a suitablesubstituted trisaryltriazine.

Of the many industrially-available polymeric materials, polystyrene, dueto its intrinsic structure, alone or in copolymers, has a markedtendency to exhibit yellow coloration which becomes increasinglyapparent on aging. It has proved to be one of the most difficult toprotect adequately against excessive discoloration, particularly thatcaused by ultraviolet radiation.

The protective method of the present invention is particularly Wellsuited for this purpose. Therefore, for purposes of this discussion,polystyrene will be taken as illustrative. Accordingly, the inventionstill further contemplates polystyrene products protected by theaddition of the protective-agent composition.

Still more specifically, the phenol derivatives used as protectiveagents in this invention may be represented by the type formula:

( a)a a)s I l (I) wherein R is an alkyl radical of from one to aboutfour carbon atoms. These compounds are not new per se and have beenpreviously known as antioxidants for oils, fats and rubber.

The substituted tris-aryltriazines of this invention may be representedby the formula:

exposure to radiation in the ultraviolet range (hereinafter abbreviatedas UV or UV-radiation).

Primarily, this has been attempted by incorporating therein smallamounts of various known UV-absorbing compounds. Such attempts have beenpartially successful over relatively short periods of exposure. However,upon continued exposure, yellowing nevertheless continues to take placeat an excessive rate. There still re mains a need for a method wherebysuch yellow discoloration may be minimized.

Further description of the present invention requires some method ofmeasuring and describing the extent of discoloration. Accordingly, fordefiinitive purposes, the effect will be discussed herein in terms ofthe yellow index (hereinafter denoted as Y.I.). This Y.I. is a measureof degree of yellowness obtained by substituting data measured by aspectrophotometer in the following formula:

wherein, T is the percent transmission of the unexposed sample at theindicated wavelength and T that of the exposed sample at the indicatedwavelengths.

Based thereon, the following test procedure was developed. To parts ofpolystyrene the amount of protective material to be tested is added on atwo-roll mill. One roll is maintained at 350 F., the other at 250 F. Themix is blended continuously over a ten-minute period by repeatedlypassing the mix through the nip of the rolls for 70 passes. Samples ofthe resultant blended mix are compression molded into a 0.050" x 2" x 2"chip. Y.l. readings are taken before and after each designated exposureperiod in the Fadeometer and the Y.I. is calculated according to theabove-noted formula. This procedure is used in the following discussionand specific examples and in obtaining the Y.I. values noted in thefollowing discussion.

It is also necessary to establish a measure of successful protection. Ingeneral, when the Y.I. exceeds a value of some 15-20 units, theresulting polystyrene is too yellow. It is considered unsatisfactory formany applications. A good result, which it is a principal object of thepresent invention to attain, is to so protect the polystyrene thatmaximum exposure periods are required before the Y.I. readings reachthis range. Less protection than about 1000 hours to Y.I.=l5 is notgenerally satisfactory. Accordingly, in the test work discussed below,unless needed for comparison, testing was stopped in most cases when aY.I. of about 20 units was obtained.

As noted above, it has been attempted previously to obtain protection byincorporation of UV-absorbers. Some benefits were obtained, but ingeneral the protection was not as sufficiently lasting as desired.Duration of protection can be extended somewhat by using larger amountsof the UV-absorber. However, this is not a generally satisfactorysolution to the problem for several reasons.

Such attempts soon encounter certain inherent limitations. For example,many known UV-absorbers produce per se an initial yellowing effect onbeing added to polystyrene. There is, therefore, a definite limit on theamount which can be added before further addition thereof offsets anyadditional benefit of increased protection. Other known UV-absorbersseem to offer good protection during initial exposure. However, whenpresent in useful amounts they tend to break down and thereafterseemingly produce an accelerated rate of discoloration.

There still remained, then, a definite need for a method of so retardingthis effect that even after prolonged exposure such yellow discolorationis minimized. Previously, such a result was not obtainable to thedesired degree by addition of UV-absorbers.

A major object of this invention, therefore, is to meet this demand; toproduce a marked improvement in the retardation of yellow discolorationand production of the resultant protected composition. As noted above,this has been accomplished by the use of the particular antioxidants incombination with the particular UV-absorbers of this invention, both incorrect amounts.

As shown in the copending application of one of us, Serial No. 161,258;filed December 21, 1961; a marked improvement in protection is obtainedby disseminating through the polystyrene some 0.01 to 1.2 weight percentof a compound of the Formula I above. These compounds, despite the factthey have no previous history as UV-absorbers and are unique inpolystyrene, produce an unexpectedly good degree of protection. Periodsof some 800900 hours to a [1. of about 15 units are obtainable.Nevertheless, a further increase in protection, if obtainable, is stilldesired. As was also pointed out therein, and in the foregoingdiscussion, the attempted use of UV- absorbing compounds alone for thispurpose encounters definite limitations and the duration of protectionremains less than that desired.

Surprisingly, in the present invention it has been found that acombination of the compounds of Formula I (above), i.e., those of theabove-noted copending application, with the substitutedtris-aryltriazine of Formula 11 (above), has an unexpected synergisticeffect on the duration of the protection. Results are obtainable whichcould not be obtained with either alone. In fact, the protection is fargreater than could be expected from the results obtainable when each isused by itself.

As was noted above, in the protective composition of the presentinvention, each of the components should be used in the correct amount.In general, the phenols of Formula I (above) may be used in amountsranging from about 0.01 to about 1.0 Weight percent of the polystyrene.However, the better practice and the preferred range is from about 0.02to about 0.5 weight percent. The trisaryltriazine of Formula II (above)may be used in amounts of from about 0.05 to about 1.0 weight percent ofthe polystryene. Again the preferred range is somewhat shorter, usuallyfrom about 0.1 to about 0.5 Weight percent.

Within the noted broad ranges, if the minimum of each is used, thetris-aryltriazinezphenol ratio will be 5:1 (a); if the maximum of each,1:1 (b). If the maximum trisaryltriazine and minimum phenol is used, theratio will be 50:1 (c). If the minimum triazine and maximum phenol istaken, the ratio would be 1:10 (d). Thus, from these figures alone, itmight be concluded that this ratio could vary from as little as 1:10 toas high as 50:1. This however, would be deceptive, the weightpercentages of the preceding paragraph represent only the actual amountswhich may be present.

Such a conclusion should not be made. The weight percentages given arethe limits for that factor alone. In addition to the use of amountswithin these limits, they should also be so selected as to maintain aproper ratio each to the other. This ratio is a further limitation inand of itself.

In general, it is better practice, as noted above, to employ a majoramount of the tris-aryltriazine and a minor amount of the phenol.Therefore, ratio (a') above, i.e., 1:10, will not be encountered inpractice. Nor should the excess be as high as in ratio above, i.e., 50:1.

In general, the ratio usually will be found to have as a practical upperlimit about ratio (a) above, i.e., :1, although it may be increasedsomewhat, if so desired. As a lower limit, it will be found that itshould be about ratio (b) above, i.e., about lzl. Moreover, in practiceit will be found in most cases that this ratio range may be shortened toform about 3.5 :1 to about 1.2: 1.

It will be found in many, if not most, cases that an Compound N0.Chemical Name li-t-butyl-p-crosol. ,6-tri-tbutyl phenol.

-dl-t-bntyl-4-cthyl phenol. -di-t-butyl-4-i-propyl phenol.-di-t-butyl-4-n-propyl phenol.(Z-hydroxyA-octyloxy-phenyl)-4,6-bis-(2,4- dimothylphenyl)-s-triazine.

B-2 2-(2-l1ydroxyl-hcxyloxy-pl1enyl)-4,6 bls(2,4-

dimcthylphenyl)striazine. 12-3z(2-hydroxy-t-butoxy-phenyl)-4,G-bis-(2,4-

dimethylphcnyl)-s-t,riazine. 2-(2-hydroxy-4-ethoxy-phcnyl)-4,G-bis-(2,4-

dimothylphenyl)-s-triazinc. 2 (2 liydroxy-4mothoxy-phenyl) -4,6-bis-(2,4-

dimcthylphenyl)-s-triazinc.

The same identification symbol refers to the same compound Wherever itoccurs in the following examples and discussion.

EXAMPLE 1 To illustrate the beneficial effect of the substituted phenolsof the above-noted copending application of one of the presentinventors, 0.1 part of the illustrative compound is mixed with partsamples of commercial polystyrene and the YE. values determined. Thetest procedure outlined above is used. Illustrative average results areshown in the following table.

Table I Exposure Hours to Y.I. Initial ol- Compound No. Y.I.

None (control) 4 200 350 520 A-l 2 510 770 825 A-2 3 650 825 955 Similarresults are obtained substituting A-3, A-4 and A-5 as the test compound.

EXAMPLE 2 In order to demonstrate the effect of using only ahisaryltriazine compound of Formula 11 (above), Example 1 is repeated,substituting 0.25 part of 8-1 for the 0.1 part per 100 of A-ll. A Y.I.of 15 is reached in about 575 hours.

EXAMPLE 3 Example 2 is repeated substituting 0.25 part of 8-2 for the B1of that example. Illustrative results are shown in the following table.

T able II Yl. after Ex osurc in 1 Protective Compound p mus) None 22 I1548 13-2 S 1 1 22 Approximately the same protection is obtained as with13-1. Substantially equivalent results are obtained in repeating theexample with B3, B-4 and B-5. As the alkyl group R in Formula II (above)decreases below about six carbon atoms, the rate of retarding theyellowing tends to fall ofi somewhat. Compounds in which R contains morethan about eight carbons do not appear to be desirable. Consequently,the compounds in which R contains six to eight carbons are preferred andB-1 in which R is octyl is used illustratively in the following example.

EXAMPLE 4 Example 1 is repeated, replacing the phenols with a protectivecomposition consisting essentially of A1 and B1 in weight ratio of 1:25.The composition is used in amounts of 0.35 part per hundred parts ofpolystyrene. Although a Y.I. of 15 is reached in only 700 hours usingA-l alone and after only about 575 hours, using the combined compositionof this example, a Y.I. of 15 is not reached when the test is stoppedafter 1200 hours.

In utilizing the present invention, it is feasible to add the twoprotective agents in succession on the mill or to add both separatelybut simultaneously. In general, however, less milling is required andgenerally better results are obtained if the two components of theprotective compositions are precombined in a uniform mixture as inExample 4 above. Moreover, this gives a larger weight to be handled andis helpful in increasing the accuracy of measurement.

When using a precombined composition as the protective agent, itscomponents should be within the ratio ranges indicated above and itshould be used in such amount that both components are present withinthe indicated Weight limitations.

We claim:

1. A polystyrene composition protected from developing excessive yellowcoloration on extended exposure to incident ultraviolet radiationconsisting essentially of homopolystyrene having dispersed substantiallyuniformly therethrough a sufiicient amount of a protective compositioncomprising a first compound of the formula z )a zh wherein R is an alkylof from one to four carbons; and a second compound of the formula (EH CHI OH wherein R represents an alkyl of from one to eight carbon atoms;said first and second compounds being present in amount sufficient toprovide from about 0.0 1 to about 1.0 part of said first compound andfrom about 0.05 to about 1.0 part of said second compound.

2. A composition according to claim 1 further characterized in that saidfirst and second compounds are present in a weight ratio of from about1:1 to about 1:5.

3. A composition according to claim 1 further characterized in that saidfirst and second compounds are present respectively in from 0.020.5 and0.1-0.5 part per parts of polystyrene.

4. A composition according to claim 1 further characterized in that saidfirst compound is tri-t-butyl phenol and said second compound is2-(2-hydroxy-4-octyloxyphenyl) -4,6-bis- 2,4-dimethylphenyl)-s-triazine.

5. A composition according to claim 1 further characterized in that saidfirst compound is tri-t-butyl phenol and said second compound is2-(2-hydroXy-4-methoxyphenyl) -4,6-bis- (2,4-dimethylphenyl)-s-triazine.

6. A composition according to claim 1 further characterized in that saidfirst compound is di-t-butyl-p-cresol and said second compound is2-(2-hydroxy-4-octyloxyphenyl) -4, 6-bis- (2,4-dimethylphenyl)-s-triazine.

References Cited in the file of this patent UNITED STATES PATENTS2,677,674 Daly May 4, 1954 2,944,998 Buxbaum July 12, 1960 2,944,999Abbruscato July 12, 1960 3,084,135 Scullin Apr. 2, 1963

1. A POLYSTYRENE COMPOSITION PROTECTED FROM DEVELOPING EXCESSIVE YELLOWCOLORATION ON EXTEDNED EXPOSURE TO INCIDENT ULTRAVIOLET RADIATIONCONSISTING ESSENTIALLY OF HOMOPOLYSTYRENE HAVING DISPERSED SUBSTANTIALLYUNIFORMLY THERETHROUGH A SUFFICIENT AMOUNT OF A PROTECTIVE COMPOSITIONCOMPRISING A FIRST COMPOUND OF THE FORMULA